Population Structure, Genetic Diversity, and Gene Introgression of Two Closely Related Walnuts (Juglans regia and J. sigillata) in Southwestern China Revealed by EST-SSR Markers

The common walnut (Juglans regia L.) and iron walnut (J. sigillata Dode) are well-known economically important species cultivated for their edible nuts, high-quality wood, and medicinal properties and display a sympatric distribution in southwestern China. However, detailed research on the genetic d...

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Bibliographic Details
Published in:Forests 2018-10, Vol.9 (10), p.646
Main Authors: Yuan, Xiao-Ying, Sun, Yi-Wei, Bai, Xu-Rong, Dang, Meng, Feng, Xiao-Jia, Zulfiqar, Saman, Zhao, Peng
Format: Article
Language:English
Subjects:
Biodiversity
common walnut
Conformation
Deoxyribonucleic acid
DNA
Edible nuts
EST-SSR
Expressed sequence tags
Genetic analysis
Genetic diversity
genetic structure
Genetic testing
Genetics
Geostatistics
introgression
Iron
iron walnut
Juglans regia
Juglans sigillata
Markers
Morphology
Population genetics
Population structure
Populations
southwestern China
Species
Species diversity
Structural analysis
Sympatric populations
Trees
Walnuts
Wood
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Summary:The common walnut (Juglans regia L.) and iron walnut (J. sigillata Dode) are well-known economically important species cultivated for their edible nuts, high-quality wood, and medicinal properties and display a sympatric distribution in southwestern China. However, detailed research on the genetic diversity and introgression of these two closely related walnut species, especially in southwestern China, are lacking. In this study, we analyzed a total of 506 individuals from 28 populations of J. regia and J. sigillata using 25 EST-SSR markers to determine if their gene introgression was related to sympatric distribution. In addition, we compared the genetic diversity estimates between them. Our results indicated that all J. regia populations possess slightly higher genetic diversity than J. sigillata populations. The Geostatistical IDW technique (HO, PPL, NA and PrA) revealed that northern Yunnan and Guizhou provinces had high genetic diversity for J. regia while the northwestern Yunnan province had high genetic diversity for J. sigillata. AMOVA analysis revealed that significant genetic variation was mainly distributed within population as 73% in J. regia and 76% in J. sigillata. The genetic differentiation (FST) was 0.307 between the two walnut species (p < 0.0001), which was higher than FST values within populations (J. regia FST = 0.265 and J. sigillata FST = 0.236). However, the STRUCTURE analysis of the J. regia and J. sigillata populations revealed two genetic clusters in which gene introgression exists, therefore, the boundary of separation between these two walnut species is not clear. Moreover, these results were validated by NJ and UPGMA analysis with additional conformation from the PCoA. Based on the SSR data, our results indicate that J. sigillata is an ecotype of J. regia. Taken together, these results reveal novel information on population genetics and provide specific geographical regions containing high genetic diversity of the Juglans species sampled, which will assist in future conservation management.
ISSN:1999-4907
1999-4907
DOI:10.3390/f9100646